In order to inhibit occurrence of accidents of vehicles that are caused by slippery road conditions, it is effective to determine whether a surface of a road is in a slippery condition or not and to inform a driver or the like of a result of determination and thus various proposals have been produced.
For instance, an apparatus in which a laser that irradiates a road surface is installed and which detects a condition of the road surface and an apparatus in which a sound sensor is installed on a vehicle and which determines a road surface condition based on noises in and around the travelling vehicle have been proposed.
Examples of the related art include Japanese Laid-open Patent Publication Nos. 2002-148184 and 2013-68986.